The present invention relates to a process for producing bulky paper which is preferably used as an absorbent base, etc. of cooking paper, paper towels, tissues, paper products for cleaning, sanitary materials, and the like.
Conventional papermaking techniques include a process comprising forming a fiber web by use of a smooth paper layer-forming belt or carrier belt having fine openings and uniformly pressing the fiber web for dewatering and a process comprising drying the fiber web by passing in hot air of a through air drier without pressing for dewatering. However, these processes have not achieved appreciable increases in paper thickness, water absorption capacity, and the like.
Known processes of producing bulky paper comprising imparting a pattern by suction to a wet fiber web before being dried, passing the fiber web (not compressed) in hot air to half dry, and finally drying in a Yankee drier include a process using a perforated patterning carrier belt having 100 to 3600 openings each having an open area of 0.0072 mm2 to 2.1 mm2 per 6.45 cm2 (see Japanese Patent Application Laid-Open No. 21405/77) and a process using a composite perforated patterning carrier belt composed of a perforated patterning resin with prescribed openings which is prepared by using a photosensitive resin and a conventional papermnaking carrier belt which reinforces the resin (see Japanese Laid-Open No. 5-506277 and Japanese Laid-Open No. 5-506893).
The process disclosed in Japanese Patent Application Laid-Open No. 21405/77 is incapable of directing softwood pulp having a relatively long fiber length toward the openings to form low-density projections.
According to the processes disclosed in WO 93/506277 and WO 93/506893, if the open area of the perforations is less than 3 mm2, the low-density projections formed by suction have an insufficient volume for obtaining sufficient thickness, water absorption capacity, and softness. Further, because the resin part of the perforated patterning carrier belt is rubbed with many reverse rolls and the surface of a Yankee drier under a strong pressure, the processes are disadvantageous from the standpoint of belt life. Furthermore, much time is required to remove or change the belt, and it is infeasible to alternate the manufacture of plain paper and bulky paper or to easily alter the pattern of bulky paper.
Accordingly, an object of the present invention is to provide a process for producing bulky paper having a large thickness, good absorption, excellent softness, and moderate strength.
Another object of the present invention is to provide a highly productive process for producing bulky paper.
Still another object of the present invention is to provide a process for producing bulky paper which copes with long-term continuous operation and allows the system to be switched to general papermaking or allows the pattern to be altered easily.
The present inventors have found that the above objects are accomplished by carrying out patterning in a patterning zone having a perforated patterning net in a specific stage of the bulky paper production process while applying a specific quantity of heat.
The present inventors have also found that the above objects are accomplished by carrying out patterning in a patterning zone having a specific perforated patterning net in a specific stage of the bulky paper production process.
The above objects are accomplished by providing a process for producing bulky paper comprising the steps of transferring a fiber web having a water content of 50 to 85% by weight to a patterning zone having a perforated patterning net revolving along a suction unit; patterning the fiber web in conformity to the perforated patterning net by sucking the fiber web which is held on the perforated patterning net while applying 5 kcal/kg or more of heat to the fiber web in a heat application zone simultaneously with or before or after the sucking of the fiber web; and then drying the fiber web in a drying zone to obtain patterned bulky paper.
The above objects are also accomplished by providing a process for producing bulky paper comprising the steps of transferring a fiber web having a water content of 50 to 99% by weight to a patterning zone which is provided before a drying zone and has a suction unit and a perforated patterning net revolving along the suction unit; patterning the fiber web in conformity to the perforated patterning net by sucking the fiber web which is held on the perforated patterning net; and then drying the fiber web in the drying zone to obtain patterned bulky paper,
the perforated patterning net comprising a reinforcing carrier belt and a perforated patterning structure which is disposed on the reinforcing carrier belt and on which the fiber web is to be built up,
the reinforcing carrier belt having an individual opening area of 0.01 to 10 mm2, an open area ratio of 10 to 70%, and a tensile strength of 20 kg/cm or more in the longitudinal direction thereof, and
the perforated patterning structure having an individual opening area of 3 to 25 mm2 and an open area ratio of 18 to 96%, a least width of 0.1 to 5 mm in the pattern-forming constituent parts thereof in the planar direction, and a thickness of 0.3 to 1.5 mm.
The above objects are also accomplished by providing a process for producing bulky paper comprising the steps of transferring a fiber web having a water content of 50 to 99% by weight to a patterning zone which is provided before a drying zone and has a suction unit and a perforated patterning net revolving along the suction unit; patterning the fiber web in conformity to the perforated patterning net by sucking the fiber web which is held on the perforated patterning net; and then drying the fiber web in the drying zone to obtain patterned bulky paper,
the perforated patterning net having an individual opening area of 3 to 8 mm2, an open area ratio of 15 to 65%, a least width of 0.2 to 5 mm in the pattern-forming constituent parts thereof in the planar direction, a thickness of 0.5 to 3.0 mm, and a tensile strength of 20 kg/cm or more in the longitudinal direction thereof